Question

Discuss the principle of estimation of phosphorus present in an organic compound.

Answer 1

Estimation of phosphorus:

In this method, a known quantity of organic compound is heated with fuming nitric acid. Phosphorus, present in the compound, is oxidized to form phosphoric acid. By adding ammonia and ammonium molybdate to the solution, phosphorus can be precipitated as ammonium phosphomolybdate.

Phosphorus can also be estimated by precipitating it as MgNH₄PO₄ by adding magnesia mixture, which on ignition yields Mg₂P₂O₇.

Let the mass of organic compound be m g.

Mass of ammonium phosphomolybdate formed = m₁ g

Molar mass of ammonium phosphomolybdate = 1877 g

Thus percentage of phosphorus = ${\displaystyle \frac{31\times {\text{m}}_{1}100}{1877\times \text{m}}}$%

If P is estimated as Mg₂P₂O₇,

Then percentage of phosphorus = ${\displaystyle \frac{62\times {\text{m}}_1\times 100}{222\times \text{m}}}$%